For better resolution in lithographic processes, an antireflective coating (ARC) material may be used to minimize the reflectivity between an imaging layer, such as a photosensitive resist layer, and a substrate. However, because the resist layer often has a composition similar that of the ARC material, the ARC material may provide poor etch selectivity relative to the imaging layer. Accordingly, since large portions of the imaging layer may be removed during etching of the ARC material after patterning, additional patterning may be required in a subsequent etching step.
However, in some lithographic imaging processes, the resist material may not provide sufficient etch resistance to effectively transfer the desired pattern to a layer underlying the resist material. In actual applications, a so-called hardmask for a resist underlayer film may be applied as an intermediate layer between a patterned resist and the substrate to be patterned. For example, when an ultrathin-film resist material is used, the substrate to be etched is thick, a substantial etching depth is required, and/or the use of a particular etchant is required for a specific substrate, a hardmask for the resist underlayer may be desirable. The hardmask for a resist underlayer film may receive the pattern from the patterned resist layer and transfer the pattern to the substrate. The hardmask for a resist underlayer film should be able to withstand the etching processes needed to transfer the pattern to the underlying material.
For example, when a substrate, such as a silicon oxide film, is processed, a resist pattern may be used as a mask. At this time, the resist may be micropatterned but with a decreased thickness. Thus, since the masking properties of the resist may be insufficient, processing of the substrate may result in damage to the substrate. Therefore, a process may be employed whereby a resist pattern is first transferred to an underlayer film for the processing of the substrate, followed by dry etching of the substrate using the underlayer film as a mask. The underlayer film for the processing of the substrate refers to a film that is formed under an antireflective film and functions as an underlayer antireflective film. In this process, the etching rate of the resist is similar to that of the underlayer film for the processing of the substrate. Thus, it may be necessary to form a mask for processing the underlayer film between the resist and the underlayer film. As a consequence, a multilayer film consisting of the underlayer film for the processing of the substrate, the mask for processing the underlayer film and the resist may be formed on the substrate.
The refractive index and the absorbance of the mask for processing the underlayer film are varied depending on the refractive index, absorbance and thickness of the underlying underlayer film for the processing of the substrate.
It is desirable that a mask for processing an underlayer film meets the following criteria: i) the mask should enable formation of a resist pattern with minimal hemming; ii) the mask should adhere well to the resist; and iii) the mask should have sufficient masking properties when the underlayer film for the processing of a substrate is processed. It is further desirable that a hardmask for processing an underlayer film exhibit high etch selectivity and be sufficiently resistant to multiple etchings. In addition, the hardmask should minimize the reflectivity between a resist and an underlying layer. Thus, the refractive index and absorbance of the mask for processing an underlayer film should be optimized to effectively utilize antireflective properties and ensure a lithographic process margin. To date, mask materials capable of meeting all these requirements have not yet been developed.